Ironstone soils are extremely restricted in distribution on the Swan Coastal Plain. These soils may have been historically associated with bogs - the iron being deposited by water percolating through the soil (H. Smolinsky1, personal communication). Restricted areas of ironstone soils associated with unusual plant communities occur in a number of areas in the southwest of Western Australia; near Kalbarri (A. Brown2, personal communication.), near Eneabba (Griffin et al. 1983), at Gingin and Busselton (Department of Environmental Protection (DEP) 1996; Gibson et al. 1994), the Scott River (Gibson et al. 2000) and near Albany (G. Keighery3 personal communication). Each of these areas contain plant communities that are characterised by different taxa.
The Perth to Gingin ironstone soil type occurs on the eastern side of the Swan Coastal Plain. This area contains heavy soils that are particularly useful for agricultural purposes and are around 97% cleared (Department of Conservation and Land Management (CALM) 1990; Keighery and Trudgen 1992). Churchward and McArthur (1980) mapped the Yanga fluviatile landform that contains these ironstone soils. The unit is described as “poorly drained plain with grey sandy benches and intervening swamps; also areas of bog iron ore, marl or solonetzic soils” (Churchward and McArthur 1980). The scale of mapping was 1:250,000, which is not sufficiently detailed to indicate the individual small areas of bog-ironstone on the Swan Coastal Plain.
On the 1:50,000 scale Urban/Environmental Geology series (Anon 1976 and 1977; Gozzard 1982) ironstone areas are noted as “bog-iron or iron-rich laterite” within the Guildford Formation, which consists mainly of alluvial clays. The original extent of the community is not known as boundaries of the soil type are not specified on these maps, but symbols occur where patches of the type occur. It is evident however, that the soil type is extremely restricted and that most of the original community has been cleared (B. Keighery4 and G. Keighery, personal communication; Gibson et al. 1994).
The Perth to Gingin ironstone soils are associated with shallow seasonal inundation with fresh water. This inundation may be from surface water that accumulates due to the impermeable nature of the ironstone and the associated heavy soils. In addition, groundwater may come very close to or may reach the surface in the wetter months.
The plant community on these ironstone soils is the only one in the Perth area that is characterised by massed everlastings (Rhodanthe spp.) in the understorey (English et al. 1996). Floristic analyses of plots on this soil type link to ‘herb rich shrublands in clay pans’ (community type 8) as described by Gibson et al. (1994), reflecting the clays in the soil (DEP 1996). Typical and common native species in the community are the shrubs Kunzea aff. recurva, Grevilleacurviloba subsp. incurva, Melaleucaviminea, Acaciasaligna, Jacksoniafurcellata, Grevilleaobtusifolia and Dryandrasessilis and the herbs Rhodanthemanglesii, Tribonanthesaustralis and Isotropiscuneifolia subsp. glabra. A full list of plant taxa currently known from plots in Occurrence 1 is provided at Appendix 1.
There is one taxon listed as rare flora under the Wildlife Conservation Act 1950, and several priority flora that occur in the Perth to Gingin Ironstone community. The largest known population of Grevillea curviloba subsp. incurva is present at Occurrence 1a (B. Keighery personal communication) and the taxon is listed as threatened (i.e. Declared Rare Flora, Endangered EPBC Act). There is an Interim Recovery Plan for Grevillea curviloba subsp. incurva (Phillimore and English 2000). There are five priority species that occur within the community, or adjacent to the occurrence (refer to the Glossary for definitions of Priority status): Isotropis cuneifolia subsp. glabra (Priority 2), Grevillea evanescens (P1), Haloragis tenuifolia (P3), Myriophyllum echinatum (P3 ) and Stylidium longitubum (P3).
The species composition of the community is likely to have been altered by grazing, as the occurrences have been grazed by stock intermittently. It is not known to what extent fire has influenced the present structure or composition of the community. The grazing would almost certainly have increased the invasion of exotic species such as Arctotheca calendula, Ursinia anthemoides, Vulpia spp., Romulearosea and Briza major into the community.
The only known occurrences of the community originally located were on private land adjacent to Airfield Road in the Shire of Gingin. The largest of these was acquired with funding from the Commonwealth National Reserve System Program and the Western Australian Government in February 1999 and is now a Nature Reserve.
Very small, degraded areas of the community occur on road reserves in the Gingin area. All of the road side occurrences except the road side portion of Occurrence 1 (refer Table 1) are considered totally destroyed as few of the taxa that were likely to have inhabited the community remain, and occurrences have been severely degraded by weeds (Gibson et al. 1994; DEP 1996).
The major threats to the community are weed invasion, grazing, inappropriate fire regimes, clearing, and possibly changes to hydrology such as salinisation and altered patterns of inundation. A recent assessment of dieback disease caused by Phytophthora spp. recorded this community as ‘uninterpretable’, as there are few if any susceptible indicator species present.
Table 1: Extent and location of occurrences
Nature Reserve 46373, Shire of Gingin
Road reserve (contiguous with 1a)
Approximately 0.25 ha
Private property, Shire of Gingin
Private property, Shire of Gingin
Table 2. Vesting , purpose and tenure of all occurrence of the Perth to Gingin Ironstone community
The ironstone community type as described by Gibson et al. (1994) and DEP (1996) was located on only one privately owned property, and adjoining road reserve, in the Shire of Gingin. Subsequently three occurrences of the community have been located on this property, and the largest, Occurrence 1a, has now been purchased by Government and is gazetted as a Nature Reserve.
Occurrence 1a consists of a shrubland dominated by Kunzea aff. recurva (swamp kunzea) and Melaleucaviminea over mixed herbs and low sedges (DEP 1996 - see Appendix 1 for species list). The herbs Rhodanthemanglesii (pink sunray) and Tribonanthesaustralis are noticeable in the herb layer in spring. Areas of Banksia woodland occur on sandy soils immediately adjacent to the western side of the occurrence. A creek line with pasture under remnant trees occurs in the north east, and pasture under remnant trees also occurs to the south. Occurrence 1a is now fenced on all sides. This occurrence is located on the shallowest soils of all the known occurrences and is associated with the greatest dominance of daisies in the understorey.
This occurrence was burnt in a hot wildfire in January 2003. Some of the overstorey vegetation was killed outright, and the remainder is resprouting from root stock. Since the fire there has been an increase in grassy and pasture weeds (L. Sage5, personal communication).
Occurrence 1b is the portion of Occurrence 1 that extends onto an adjacent road reserve, where the community has been degraded in terms of a decline in floristic diversity, and subsequent dominance by weeds. This road reserve portion of Occurrence 1 was historically slashed. Pasture-land occurs on the opposite side of the road.
Occurrence 2 is about a kilometre north of Occurrence 1. The shrub layer in both Occurrences 2 and 3 consists of a thicket dominated by Kunzea aff recurva and Melaleucaviminea. The herb layer in these two areas contains a similar suite of species to Occurrence 1. Occurrence 2 covers about two hectares within a 12 ha remnant. The remainder of the area is Banksia woodland and a densely wooded wetland. The land owner had erected an electric fence around the perimeter of the entire remnant, as he recognized the vegetation as significant. In 2004, DEC re-fenced the whole 12 ha remnant with standard ringlock fence, in consultation with the landholder.
Occurrence 3 is within a larger remnant that is surrounded by an electric fence and used as a bull paddock. The surrounding area consists of remnant trees over pasture. This occurrence is about 750 m south of the northern edge of Occurrence 1, and about 500 m east of that occurrence. It is proposed that this area will also be fenced, in liaison with the landholder.
Ironstone soils occur elsewhere in the vicinity of this occurrence, but are either totally cleared or support a community that has been so modified as to be considered totally destroyed (Gibson et al. 1994; DEP 1996).
Data on all known occurrences of threatened ecological communities are held in the threatened ecological community database at DEC, kept at the Wildlife Research Centre, Woodvale.
Biological and ecological characteristics
The ironstone soils near Gingin are seasonally inundated (surface water in wetter months). Many of the plant species present are specifically adapted to this shallow seasonal inundation, eg., Kunzea aff. recurva (swamp kunzea) and the herb layer that appears in late winter and early spring. This herb layer is a major distinguishing characteristic of this community.
The daisy-dominated herb layer that is characteristic of this community does not occur on adjacent deeper soils This is likely to be because species that reproduce by means other than annual seed production may have a competitive advantage (G. Keighery, personal communication). Indeed, the herb assemblages on the ironstone soils where the topsoil is deepest are not dominated by daisies, although daisies still occur (Occurrences 2 and 3; V. English, J. Blyth6, personal observation).
Local hydrogeology is likely to be very important in maintaining the shrublands and woodlands of the Perth to Gingin Ironstone community. The hydrology of the occurrences is most likely to be influenced by the interactions of regional and local groundwater flows, and surface flows. There is little information available about these hydrological interactions, however, some information can be gleaned from data held in the literature, and from direct observations.
Long term observations (G. Keighery and B. Keighery; landholder, personal communication) indicate that seasonal inundation is limited to very shallow surface water during the winter months. Inundation usually persists for a period of around three months, with the soils drying out at the surface in summer. The surface waters may be linked to the water table as the groundwater is close to the surface in September - October (Davidson 1995). Surface water would also originate from rainfall runoff in the wetter months of the year and be retained by the impervious substrata of heavy soils and rock. If there are connections between the surface and groundwater through the ironstone, then both these sources would affect the quantity and quality of water on the surface of the site.
Occurrences of the community are all located on the north Gnangara Mound, an unconfined groundwater aquifer. The height of the groundwater table is 60-70 metres above sea level (m AHD) where the community occurs. Occurrences are also located in a low point adjacent to a peak in the water mound (a ‘col’) and adjacent to a flow channel in the groundwater mound (Davidson 1995).
A trend of falling water tables in the general area is evident since around 1976 (Greay 1993). As there is a corresponding decline in annual rainfall this general fall in the water table may be presumed to be at least partly as a result of this decline. It is possible that draw-down of the superficial aquifer - the Gnangara Mound - could also have had an effect. The hydrology of specific areas of the eastern side of the Swan Coastal Plain has also been altered through the construction of drains to lower the water table (Keighery and Trudgen 1992). Conversely, the area is characterised by much valued heavy soils, which were historically highly cleared for agriculture, and for the Gingin Airfield immediately to the west. Clearing is likely to have increased surface runoff and recharge of the groundwater in the local area. Despite a likely increase in recharge due to clearing, drainage has probably resulted in an overall lowering of the water table in localised areas (B. Keighery personal communication). Altered surface flow and/or alteration of the height of the local water table may change the length of the period or the depth of ponding.
The shallow groundwater in the vicinity has a salinity of around 250-500 milligrams per litre total dissolved solids (mg/L TDS) (Davidson 1995), which is quite fresh. Areas of fresh groundwater are generally associated with relatively low risk of salinisation on the Swan Coastal Plain (Davidson 1995). However, samphire, which is vegetation associated with saline areas, was recorded very close to Occurrence 2 (J. Blyth, N. Gibson7, V. English, personal observation).
The Central Coast Regional Strategy (WA Planning Commission 1996) indicates there is unlikely to be significant urbanisation in the area due to the proximity to the airfield. Additional water table rise in the superficial aquifer or increased surface flows due to further clearing in the catchment therefore seem unlikely. This issue is discussed further under threatening processes.
Habitat critical to survival, and important occurrences
The habitat critical to the survival of the Perth to Gingin Ironstone community comprises:
the area of occupancy of known occurrences;
areas of similar habitat surrounding known occurrences, i.e. poorly drained flats, depressions or winter wet flats with shallow red brown sands and loams over massive ironstone
remnant vegetation that surrounds or links occurrences (this is to provide habitat for pollinators or to allow them to move between occurrences); and
the local catchment for the surface and groundwaters that maintain the winter-wet habitat of the community (the plant community would be dependent on maintenance of the local hydrological conditions).
Given that the community is listed as Critically Endangered, it is considered that all known occurrences, and the catchments for the surface and groundwater that support the community, are critical to the survival of the community.
Benefits to other species/ecological communities
The largest known population of Grevillea curviloba subsp. incurva is present at Occurrence 1a (B. Keighery personal communication) and is listed as threatened (i.e. rare flora) under the Wildlife Conservation Act 1950. There is an Interim Recovery Plan for Grevillea curviloba subsp. incurva (Phillimore and English 2000). There are five priority species that occur in the community (Atkins 2005, refer to the Glossary for definitions of Priority status): Isotropis cuneifolia subsp. glabra (Priority 2), Grevillea evanescens (P1), Haloragis tenuifolia (P3), Myriophyllum echinatum (P3 ) and Stylidium longitubum (P3).
Recovery actions implemented to improve the quality or security of the community are likely to improve the status of any species within the community.
This plan is fully consistent with the aims and recommendations of the Convention on Biological Diversity and will assist in implementing Australia’s responsibilities under that Convention. This community is not specifically listed under any international treaty and therefore this plan does not affect Australia’s obligations under any other international agreements.
Role and interests of indigenous people
Involvement of the indigenous community has been sought through the advice of the Department of Indigenous Affairs to determine whether there are any issues or interests identified in the plan. Department of Indigenous Affairs Aboriginal Heritage Sites Register has no sites listed within this Ironstone community and no indigenous interests have been identified for the areas that contain the community. Where no role is identified for the indigenous community in the development of the recovery plan, opportunities may exist through cultural interpretation and awareness of the ecological community. Indigenous involvement in the implementation of recovery actions will be encouraged.
Social and economic impacts
Two occurrences occur on private land, and part of one occurrence is managed by the Shire of Gingin. Negotiations will continue with the land managers with respect to the future management of these occurrences.
The implementation of this recovery plan has the potential to have some limited social and economic impact, where occurrences are located on lands that are not specifically managed for conservation. Recovery actions refer to continued liaison between stakeholders with regard to these areas.
Occurrences of the Perth to Gingin Ironstone community occur within the local government authority of the Shire of Gingin. They occur on land managed by the Shire of Gingin, DEC, and on land managed by one private land owner.
Historical and current threatening processes
Clearing for agriculture has been extensive on the heavy soils on the eastern side of the Swan Coastal Plain, with some 97% of all vegetation in the area cleared historically (Keighery and Trudgen 1992; CALM 1990). The vegetation on the ironstone soils near Perth occur on this portion of the plain and has suffered almost total destruction.
The largest remnant of the community (Occurrence 1), adjacent to Airfield Road, was apparently rolled and fertilised in 1969. However, the attempt to convert the area to more useable pasture was not successful as the soils were too shallow (landowner, personal communication).
Grazing of the community is likely to have caused alterations to the species composition, by the selective grazing of edible species, the introduction of weeds and nutrients, trampling, and general disturbance.
Occurrence 1 was grazed by livestock for many years prior to the land becoming a conservation reserve. The shallow soils are not very productive and the area was historically only lightly grazed as a consequence. Grazing was reduced when the area became a nature reserve and ceased with the erection of the subsequent permanent fencing in 2004. Kangaroos and rabbits still have access onto the reserve for grazing, and this may affect regeneration.
The most northerly remnant (Occurrence 2) was permanently fenced from stock by DEC in 2004. Fencing was very difficult in the ironstone soils. Occurrence 3 is basically fenced within a larger area that is used as pasture and is currently lightly grazed as a bull-paddock (landowner, personal communication). DEC will seek to fence this remnant in consultation with the landholder.
Altered fire regimes
As this community is not well studied, little is known of its requirements in terms of fire regime to maintain species composition. The current study of the 2003 wildfire impacts on species composition and regeneration will provide data about the community’s response to fire.
Mediterranean ecosystems are usually fire responsive and indeed may require a particular fire regime to assist regeneration (Abbot and Burrows 2003). If an appropriate fire frequency is exceeded, however, species that are obligate seeders may not have sufficient time to flower and produce seed. If the time between fires is too long, obligate seeders may senesce and be unable to regenerate. Therefore, wildfires or prescribed burns must occur at appropriate intervals, and possibly at the appropriate season and intensity, to sustain the integrity of plant communities.
Too frequent fire can increase the risk of invasive weeds establishing within small bushland remnants such as this community (Abbot and Burrows 2003). Following the hot wildfire in January 2003, there was an observable increase in grass and pasture weeds (L. Sage, personal communication).
Grazing alters species composition through increased nutrient levels and weed invasion. Other disturbances, such as fire and disturbance of the vegetation also result in increased weed invasion. The pollution of the surface waters with droppings from stock is likely to cause increased nutrient levels and, hence, to favour weed species, which are generally adapted to higher levels of nutrients than local species.
A weed control program would be necessary to maintain or improve the current condition of occurrences of the community in the long term. Brown and Brooks (2002) state that the generic aims of weed control are to maintain the pre-invasion condition of the habitat (prevention), control or arrest ongoing weed invasion (intervention), and reverse the degraded condition of the habitat where applicable (rehabilitation). A generic weed control program would involve the following steps (adapted from Brown and Brooks 2002):
1. Accurately mapping the boundaries of weed populations.
2. Selecting an appropriate herbicide or other method of weed control after determining which weeds are present.
3. Controlling weeds that pose the greatest threat to the community in the early stages of invasion where possible, e.g. invasive perennial grasses, Watsonia.
4. Rehabilitation through reintroduction of local native species where areas are no longer capable of regenerating following weed control.
Increased clearing would be expected to result in increased runoff and an increase in recharge to the groundwater table. Alternatively, drainage of the area and uncontrolled abstraction from irrigation bores may lower groundwater levels, especially in summer. Altered periods or depths of ponding may impact the timing of growth of herbs in the understorey, and may also affect the species composition of the community by favouring different plant species.
Salinisation may pose a threat to this ironstone community as it occurs on very low-lying, seasonally inundated sites. Samphire, which is vegetation associated with saline areas, was recorded very close to Occurrence 1 and Occurrence 2 (Ecoscape 2004; J. Blyth, N. Gibson, V. English, personal observation). It is not known if this is a result of natural salinity arising from the annual drying out and concentration of small amounts of salt in rain water, or secondary salinity as a consequence of clearing in the catchment.
The levels of salinity in the community will ideally be monitored to determine if salinisation poses a major threat to the community. Remedial actions such as replanting with deep rooted vegetation in strategic parts of the catchment may be indicated if monitoring shows that secondary salinisation is a problem.
Erosion by wind and water
Erosion by wind and water may also occur following removal of vegetation by clearing, grazing or fire, although it may not be significant for this community, which is located on heavy soils.
This plant community is believed not to be susceptible to dieback from Phytophthora cinnamomi as there are very few dieback indicator species within the community. In 2004 this community was recorded as ‘uninterpretable’ in a dieback assessment. However, even if it is likely to be affected the occurrences should be treated as uninfested.
Another plant community that occurs on ironstone soils in the Busselton area (‘shrublands on southern ironstones’ - community 10b as identified by Gibson et al. 1994) is extremely susceptible to dieback, but the species composition of the two ironstone communities is very different.
Risk of introduction of disease in this community should be minimised by undertaking the appropriate hygiene procedures. This would involve wash-down of any equipment used adjacent to the community, and restricting access by vehicles and machinery to dry soil conditions.
Evaluation of the Plan's Performance
DEC, in conjunction with the Swan Region Threatened Flora and Communities Recovery Team, will evaluate the performance of this Interim Recovery Plan. The plan is to be reviewed within five years of its implementation. Any changes to management / recovery actions will be documented accordingly.
1.2 Conservation status
The community meets the criteria for Critically Endangered (CR) as follows (from CALM 2005):
A) The estimated geographic range, and/or total area occupied, and/or number of discrete occurrences since European settlement have been reduced by at least 90% and the following applies:
ii) modification throughout its range is continuingsuch that in the immediate future (within approximately 10 years) the community is unlikely to be capable of being substantially rehabilitated.
B) Current distribution is limited, and the following applies:
ii) there are very few occurrences, each of which is small and/or isolated and extremely vulnerable to known threatening processes;
C) The ecological community exists only as highly modified occurrences that may be capable of being rehabilitated if such work begins in the immediate future (within approximately 10 years).
1.3 Strategy for recovery
To identify, and influence the management of, the areas in which the community occurs, so maintaining natural biological and non-biological attributes of the sites and the current area covered by the community.
To conduct appropriate research into the ecological characteristics of the community to develop further understanding about the management actions required to maintain or improve its condition.